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# to you under the Apache License, Version 2.0 (the
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#   http://www.apache.org/licenses/LICENSE-2.0
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from __future__ import annotations

from typing import TYPE_CHECKING, TypeVar

if TYPE_CHECKING:
    from typing_extensions import TypeIs

    T = TypeVar("T")

__all__ = ["NOTSET", "ArgNotSet", "is_arg_set"]


class ArgNotSet:
    """Sentinel type for annotations, useful when None is not viable."""


NOTSET = ArgNotSet()
"""Sentinel value for argument default. See ``ArgNotSet``."""


def is_arg_set(value: T | ArgNotSet) -> TypeIs[T]:
    return not isinstance(value, ArgNotSet)
